Torque Converter Rattle?

[truckster]

I have a new (less than 6000 mile) 5.7 Vortec in my 72 Blazer. I balanced and blueprinted the engine and assembled it myself, so I'm confident that's not my problem. I mated it to the existing TH350 transmission and reused the torque converter, because it was working fine before I pulled the engine... seven years ago (I probably should have thought that one through better). I should mention that I used a new Jegs SFI heavy-duty flexplate.

In the past few weeks it's picked up a rattling sound when I first start it. My first thought was to check the torque converter bolts and the bellhousing bolts - they're all good and tight. I also have what I would describe as something like a squealing sound around 2000 RPM, and it seems to only occur in a narrow RPM range.

I crawled under it again today, and I'm pretty sure it's coming from the torque converter. Two questions - does my diagnosis seem accurate, and how long is it likely to last before it strands me or does some serious damage?

Thanks!